Generally, Single-track vehicles (motorcycles, scooters, mopeds and bicycles) enjoy significant advantage over dual-track vehicles (such as cars) in terms of handling (i.e. maneuverability, acceleration, slalom) and energy efficiency. It is obvious when we compare a typical single-track vehicle with a typical car: The payload to vehicle weight ratio is 1/20 for a car, while a typical single-track vehicle (i.e. motorcycle) has a payload to vehicle weight ratio of 1/2, a factor of 10 better. Although automobiles are typically a very popular choice for tens of millions of commuters everyday, it may be the most energy inefficient among all man made transportation tools. Carrying of single individual of 150 lb by a vehicle of 3000 lb is simply gross waste of precious energy resources. Due to their large front profile and four wheels, cars consume much of their power by the large aerodynamic drag force and large tire friction force at high speed. Cars are also much wider than single-track vehicles and need a relatively wide road to operate. As a result the road system occupies large land resource and is expensive to build for reasonable flow capability. Energy and time wasting, environment damaging traffic jams are frequent at large metropolitans during rush hours. The parking lots also have to be large enough to accommodate the vehicle sizes. All these contribute to large and wasteful land usage. The excessive weights of vehicles are also dangerous. Dual-track vehicles take much more brake force to stop them. In addition, dual-track vehicles also produce a much larger impact force in an accident. The energy, environment and land resource issues are compounding in the densely populated developing countries. The transportation needs of tens of billions of people cannot be met by automobiles due to the large burdens on the energy, environmental and land resources.
The tremendous reduction of body weight of a single-track vehicle makes its engine much more effective in propelling it to a reasonable acceleration and speed even with a much smaller engine power. Single-track vehicle can also be more energy efficient in reduction of aerodynamic-drag, which is a major energy consumption contributor at high speed. Since the front profile is much smaller than that of a typical car with an elongated body, single track-vehicle has much smaller aerodynamic drag force. Combining this with the fact that most single-track vehicles have two main wheels, single-track vehicle can cruise at high speed with much reduced energy consumption rate. They are also environmentally friendlier, use less road and parking resources and release less greenhouse gas. But typically, single-track vehicles require extensive skill to ride and are considerably more dangerous for inexperienced riders due to their intrinsic instability. As a result, the mass population does not realize the potential for high fuel efficiency, environmental safety and high performance of single-track vehicles.
Several types of light vehicles have been proposed to address the above issues through either inline two wheels (i.e. motorcycle) with two supporting wheels or three wheels (tricycle). The first type still requires rider to keep balance in normal riding condition when the supporting wheels are retracted. Therefore, in general, it still requires complex skill to ride it. The second type is a compromising solution between car and motorcycle: It has three wheels to keep balance during slow or stop condition. At high speed some them can balance the vehicle via active tilt control. For example, in U.S. Pat. No. 5,765,846 (1998) to Braun from Daimler-Benz, U.S. Pat. No. 5,762,351 (1998) to Soohoo and U.S. Pat. No. 4,903,857 (1990) to Klopfenstein. Europe and Japan also granted quite a few patents on this area: 560,670 (European Patent Office) to Putin (1995) and U.S. Pat. No. 5,039,073 to Matsuura from Honda motor (Japanese Patent). This type of vehicles are self-balanced like cars. But they are heavier compare with motorcycles, more expensive to make due to their energy drain hydraulic active tilt control of the vehicle body and consume more power due to increasing of tire road friction from the extra wheel. The self-balanced vehicle Segway uses two wheels (left and right) with a dynamic balance to keep vehicle from falling forward or backward. (U.S. Pat. No. 5,971,091 to Kamen et al). The major limitation is its speed and distance between charges. Due to the centrifugal force during turn and high center of gravity, Segway cannot go fast during turn. That is why its top speed is less than 20 mph.